Effects of Lactobacillus plantarum Ep-M17 on growth performance, immune response, and intestinal flora of the Plecoglossus altivelis (Ayu)

The increasing use of probiotics as functional feed supplements in aquaculture has spurred extensive research into their health-promoting properties. This study investigated the protective effects of Lactobacillus plantarum Ep-M17 in Plecoglossus altivelis (Ayu), building on previous findings of its antibacterial activity against Pseudomonas plecoglossicida. Dietary supplementation with Ep-M17 significantly enhanced various aspects of fish health and performance. The probiotic improved growth parameters and feed utilization efficiency while providing substantial protection against pathogenic infection, as evidenced by a 61.1 % relative protection rate during challenge trials. Comprehensive analyses demonstrated that Ep-M17 strengthens intestinal barrier function by promoting villi development and maintaining mucosal integrity. The probiotic stimulated systemic immune responses through the activation of key enzymes such as α-AL, LPS, AKP, CAT, LZM, and SOD, and cytokine pathways including IL-1, IL-10, TGF-β1, TNF-α, IgM, and IFN-γ in the liver, intestine, spleen, and kidney. Notably, microbial community analysis revealed Ep-M17's ability to modulate gut microbiota composition, specifically increasing beneficial bacteria such as Cetobacterium spp. and Bacillus spp. While reducing pathogenic Pseudomonas populations. These combined effects enhanced the host's nutritional status, immune defenses, and microbial balance. The study highlights Ep-M17's potential as an effective alternative to antibiotics in aquaculture, demonstrating its ability to simultaneously address growth promotion and disease prevention through integrated physiological effects. These findings support the use of targeted probiotic strategies for sustainable aquatic health management.